DEFINITION OF
SALIENT ELECTRICAL TERMS
1. Electricity: Electricity
is a form of energy, which is invisible but it can be felt by some of its
effects, such as lighting effects, heating effects, magnetic effects, chemical
effects, etc.
2. Voltage: It is the
electrical pressure which makes the electric current (electrons) to flow in the
circuit. The unit by which voltage is measured is called Volt.
In A.C., we have single phase supply 230V and three phase supply
400V. Normally single phase supply is given for lighting loads and three phase
supply for power intensified loads.
Low medium, High and Extra High Voltage:
Upto 250 Volts, it is called low voltage.
Upto 650 Volts, it is called medium voltage.
Upto 33,000 Volts, it is called high voltage (HV).
Voltage exceeding 33,000 Volts is called extra high voltage (EHV)
3. Current: Flow of
electrons in any conductors is called Current. the unit by which the current is
measured is called Ampere. There are two types of Electric current. viz.,
Direct and Alternating Current.
Direct Current: It is unidirectional current which changes its magnitude but
not the direction.
Alternating Current: It is the current which changes its magnitude and
direction periodically.
4.Resistance: It is the
property of a substance which does not allow the electricity to pass through
it. The unit used to measure the resistance is called Ohm.
5. Watt: It is the
unit used for measuring electric power. The product of Volt, ampere and the
power factor is watt.
Kilowatt Hour: The unit used to measure electrical energy is called Kilowatt
Hour. This is the product of the electric power used in kilowatts and the No.
of hours of power was utilized. The consumption bill sent to L.T. consumers is
based on kilowatt hour (KW Hr.)
6. Short Circuit: When positive
and negative or phase and neutral wires meet each other (bare conductor)
without any resistance, then it is called short circuit. High current will flow
due to this and cables will be over heated.
Short Circuit leading to overheating of cables will result in meeting of the
cables with fuse blowing out causing strain to the Board's equipments.
7. Fuse: Fuse is the
weakest point if an electrical circuit that may cut the circuit when an
abnormal current flows. It is therefore very essential that fuse wire is
provided for safety of machines and persons.
Lead or Tinned Copper is used for fuse wires.
If no fuse is provided in an electrical circuit, in the event if short circuit,
high current will flow in the circuit, which will heat the cables and there
will be danger or fire.
8. Earth: A solid wire
coming from an electrode driven 2.5 to 3 meters deep into the ground is called
earth.
Earthing is done to save human life from danger of electric shock and death by
blowing the fuse of the apparatus which become leaky (faulty).
A good earthing gives very low resistances to the flow of whole current of a
circuit.
Double earth is necessary for all three phase machines for the following
reasons:
(a) To give low resistance.
(b) If one earth is out of order, the second will do the work.
9. Capacitor: It is a
static device consisting of two metallic plates insulating by a dielectric
medium. This dielectric medium can be air, paper or polypropylene
The capacity of a capacitor is expressed in terms of KVAR.
10. Generator: This is an
appliance which converts mechanical energy into electrical energy. The
mechanical energy is produced by a prime mover, like, diesel engine, steam
turbine, etc.
D.C. generators are called Dynamos and AC generators termed Alternators.
11. Transformer: This is a
static machine which converts high voltage into low voltage and vice versa,
without change in supply frequency.
12. Frequency: The rate at
which the no. of cycles are performed in one second is termed as frequency. The
standard frequency for AC supply in India is 50 cycles/sec.
THE ELECTRICAL WIRES, CABLES, APPLIANCES AND
PROTECTION DEVICES AND
ACCESSORIES (
QUALITY CONTROL) ORDER 2003.

No
person shall by himself or through any person on his behalf manufacture or
store for sale, sell or distribute any electrical wires, cables, appliances,
protection devices and accessories which do not confirm to the Specified
Standards and do not bear Standard Mark of the Bureau on obtaining
certification marks Licence: 
PRODUCTS

S.No

Item

Standard

1

Safety of
Household and similar electrical AppliancesElectrical immersion water
Heaters

IS
302 –2 201 (1992)

2

Safety
of household and similar electrical Applicances – Electric iron

IS
302 – 2 –3 (1992)

3

Safety
of household amd similar electrical Applicances – Electric stoves

IS
302 –2202 (1992)

4

Safety
of household amd similar electrical Applicances – Electric raditors

IS – 3022 –
30 (1992)

5

Switches
for domestic and similar prposes

IS
3854:1988

6

2
Amp switches for domestic and similar purposes

IS
4949:1968

7

Tungsten
Filament General Services Lamps

IS
418

8

Electrical
Accessories – Circuit Breakers for over current portection for house hold
and similar installations

IS
8828

9

Residual
current operated circuti breakers for household and similar uses (pt.1):
ircuit breakers without intergral overcurrent Protection (RCCBs)

IS 12640
(pt.1)

10

Residual
current operated circuit breaker for household and similar uses (pt.2):
Circuit breakers without Intergral overcurrent Portection (RCVOs) switching
elements.

IS
12640 (pt.2)
IS 13947
(pt.5)

11

PVC
insulated cables for working voltages upto and including 1100V

IS
694

12

Elastomer
insulated cable (pt.1) for working voltages upto and including 1100 V

IS 9968
(pt.1)

13

AC
Watthour meters, class 0.5, 1 & 2 (KWH)

IS
13010

14

AC
static Watthour meters, class 0.5, 1 & 2 (KWH)

IS
13779

15

Acstatic
transformer operated watthour and VAR – hour meters, class 0.2S & 0.5S

IS
14697


IMPLIMENTING AUTHORITY

The Electrical Wires, Cables, Appliances and
Protection Devices and Accessories ( Quality control) Order 2003. GOVERNMENT
OF KERALA Power (A) Department NOTIFICATION

G.
O.(Rt.) No. 236/2004/PD Dated: Thiruvanthapuram  7th June, 2004
S.R.O. No. 606/2004 In exercisf of the powers conferred by sub
clause (b) Clause 2 of the electrical wires, Cables, Appliance, an rotection
Devices and accessories ( Quality contoll) Order, 2003 publiched as
notification No. S.O.189(E) in the Gazette of india extraordinary, part II
Section 3, Sub Section (ii) No. 159 dtd. The 17thday of February, 2003, the
Geoverment of Kerala Herby appoint the Chief Electrical Inspector, Additional
Chief Electrical Inspector, Deputy Chief Electrical Inspector and Eelectrical
Inspector as the appropriate authutity to implement the provisions of the
said order.
By order of the Governor
Principal Secretary to Government

THE
ELECTRICAL WIRES, CABLES APPLIANCES AND ACCESSORIES (QUALITY CONTROL)
ORDER 1993
I
As per
above order following thirty three items of Household Electrical
Appliances shall not be manufactured, stocked for sale without obtaining
manufacturer's certificate from Appropriate Authority of the State where
the item is being manufactured.
Item No.

Electrical
Appliances

Standard

1.

Storage
type Electric Water Heater

IS:20821985

2.

Elastomer
insulated cables PartI (for working voltage upto and including 1100
Volts) (For Welding cables refer IS:98571981)

IS:99681988

3.

Elastomer
insulated cables PartII (for working voltages for 3.3 KV upto and
including 11KV (For welding cables refer IS:98571981)

IS:99681981

4.

PVC
insulated cables for working voltage upto and including 1100 Volts

IS:6941977

5.

Polyethylene
insulated cables for working voltages upto and including 1100
Volts

IS:15961977

6.

Electric Hot Plates

IS:3651983

7.

Domestic Electric Food Mixers (Liquidizers and Grinders)

IS:42501980

8.

Electric Toasters

IS: 12871986

9.

Electric Coffee Parcolators (Non regular type)

IS: 35141966

10.

Electric Kettles and Jugs for Household and similar use

IS: 3671983

11.

Domestic Electric Clothes Washing Machine

IS: 63901983

12.

Electric Water boilers

IS: 34121985

13.

Mains operated Electric Hair Dryers

IS: 71841973

14.

Mains operated Electric Shavers

IS: 51591969

15.

Domestic Electric Cooking Ovens

IS: 57901985

16.

Steam Irons

IS: 62901986

17.

Flexible Electric Heating Pads for domestic use

IS: 51611969

18.

Portable handhold Mains Operated Electric Massagers

IS: 71371973

19.

Portable low speed Food Grinding Machines

IS: 76031975

20.

Appliances connectors and Appliances inlets
(Nonreversible 3 pin type) Appliances. Connector Part I.

IS: 30101965

21.

Appliances connectors and Appliances inlets
(Nonreversible 3 pin type) Appliances. Connector Part II.

IS: 30101965

22.

Thermostats for use with Electric Water Heaters

IS: 30171985

23.

Cartridge type Heating Elements (Non Embedded type)

IS: 37241966

24.

Resistance Wires, Tapes and strips for Heating Elements

IS: 37251966

25.

Solid embedded type Electric Heating Elements

IS: 41581985

26.

Mineral filled sheathed Heating Elements

IS: 41591983

27.

Thermostats for general purpose Electric Ovens

IS: 41651967

28.

MicaInsulated Heating Elements

IS: 64461986

29.

Electric Portable Lamp Stands and Brackets

IS: 34811966

30.

3 Pin plugs made of resilient materials

IS: 65381971

31.

Bayonet Lamp Holders

IS: 12581987

32.

Electric Instantaneous Water Heaters

IS: 89781985

33.

Single Walled Baking Ovens

IS: 89851975


(G.C.P.) Ed 2910A(3000493)
II
Following Seven items of
Household Electrical Appliances shall not be manufactured, stocked for
sale, or sold without obtaining ISI mark granted by Bureau of Indian
Standards.


1.

Electric Iron

IS: 30223 (1992)

2.

Electric immersion water heater

IS: 3022201(1992)

3.

Electric Stove

IS: 3022202(1992)

4.

Electric Radiator

IS: 302230(1992)

5.

Switches for domestic and similar purposes

IS: 38541988

6.

2 Amp switches for domestic and similar purposes

IS:49491968

7.

3 pin plugs and socket outlets

IS:12931988


III
The General Service Electric
Lamp : Quality Control) Order 1989.
The Following item of Household Electrical Appliances shall not be
manufactured, stocked for sale, or sold without obtaining ISI mark
granted by Bureau of Indian Standards.


1.

General Service Electric Lamps

IS: 4181989




GUIDELINES FOR CONSERVATION OF ELECTRICAL ENERGY
Conservation
of electrical energy has become the challenge of today. Reduction in demand
through efficient utilization of energy and waste reduction may be deemed as
"energy conservation".
The easiest
and quickest methods is by way of adopting simple measures immediately by all
sectors of power consumers without involvement of cost.
Immediate
Measures
The salient
immediate measures to be followed by Domestic, Commercial and industrial
consumers are given below:
Domestic
Sector
1. Switch off
lights, fan, coolers, air conditioners and heaters when not required.
2. Make greater use of day light for illumination and avoid use of electrical
light during day time.
3. Accumulation of dust and soot reduce the useful output. Keep lamps and
fixtures free from dust and soot.
4. Avoid use of energy for decorative lighting. Switch off all the lights other
than those needed for security when building is unoccupied.
5. Repair leaks and insulate the pipes of hot water supply.
6. Minimize opening of fridge doors to the extent possible.
Commercial
Establishment
1. Switch off
water coolers at the end of normal business hours.
2. Reduce the number of the lifts in service during hours when most occupants are
not leaving or entering building. Switch off the electrical mechanism for the
lifts not in use.
3. Encourage persons walk up and down one flight of stairs rather than use the
lift.
Industrial
Sector
1. Tighten the
belt and pulley at required intervals to reduce losses due to slip.
2. Lubricate motors and drives regularly to reduce friction.
3. The motors should be cleaned to facilitate proper cooling.
4. Heat losses in furnace can be reduced by minimizing opening of doors.
UNITS OF ELECTRICAL ENERGY CONSUMED BY COMMON DOMESTIC
APPLIANCES / EQUIPMENTS
Electrical
Appliance

Wattage
Rating

Time for 1
Unit of Consumption

Incandescent Bulb

25 W

40 hrs

Incandescent Bulb

60 W

25 hrs

Incandescent Bulb

100 W

10 hrs

Fluorescent Tubelight 2 ft

20 W

50 hrs

Fluorescent Tubelight 4 ft

40 W

25 hrs

Night Lamp

15 W

66 hrs 40
mins

Mosquito Repellent

5 W

200 hrs

Fan

60 W

16 hrs 40
mins

Air Cooler

170 W

5 hrs 50
mins

Air Conditioner (11.5 Ton)

15002500 W

40 to 30
mins

Refrigerator (165 litres)

100 W

10 hrs

Mixer/Blender/Juicer

450 W

2 hrs 15
mins

Toaster

800 W

1 hrs 15
mins

Hot Plate

10001500 W

1hr 40 mins

Oven

1000 W

1hr

Electric Kettle

10002000 W

1 hr to 30
min

Iron

450700 W

2 hrs 15 mins
to 1 hr 25 mins

Water Heater 1 1/2 2 litre
capacity (Instant Geyser)

3000 W

20 mins

1020 litre (storage type)

2000 W

30 mins

Immersion Heater

1000 W

1 hr

Vacuum Cleaner

700750 W

1 hr 20
mins

Washing Machine

325 W

3 hrs

Water Pump

750 W

1 hr 20 mins

Television

60120 W

16 to 6 hrs

Radio

15 W

66 hrs 40
mins

Video

40 W

25 hrs

Tape Recorder

20 W

50 hrs

Stereo System

50 W

20 hrs

Note: Wattage
ratings given above are only indicative
Please avoid using heavy domestic appliances between 6 and 9 both in
morning and evening. There are Peak Hours when power consumption should
be minimized.



CURRENT
RATING FOR COPPER & ALUMINUM CONDUCTORS VULCANIZED RUBBER, PVC OR
POLYTHENE INSULATED CABLES (SINGLE TWIN, THREE & FOUR CORE)
Item

Standard
Copper Conductor


Continuous
Current Rating (Subject to Voltage Drop) (Amps)

Standard
Aluminium Conductor

Area
(Sq. In)

Strand
(Inch)

In
conduit troughing or casing (2 single Core Cables)

Bunched
in Free Air or Open Trench

One
Twin
Core
DC or AC

One 3 or
4 Core Cable Balanced 3 Phases

Area
(Sq. mm)

Strand
(mm)

2 Single
Core Cables

3 or 4
Core Cables

1

0.0015

1/004

5

5

5

5

5





2

0.002

3/.029

10

10

10/9

10

8/7

1.5

1/1.40

3

0.003

3/.036

15

15

13/12

15

10/11

2.5

1/1.80

4

0.0045

7/029

20

20

15

20

15





5





20

20

17

20

14

4

1/2.80

6





27

27

24

27

19

6

1/2.80

7

0.007

7/.052

28

28

25

28

20





8





34

34

31

34

24

10

1/3.55

9

0.01

7.044

36

36

32

36

25





10

0.0145

7/052

43

43

39/38

43

30

16

4/1.70

11

0.225

7/.64

53

53

48

53

37





12





59

59

54

59

42

25

7/2.24

13

.03

19/044

62

62

56

62

43





14





69

69

62

69

48

35

7/2.50

15

0.04

19/052

74

74

67

74

52





16







91

82

91

62

50

7/3.00

17

0.06

19/064



97

88

97

68





18

0.075

19/0.072



123

107

115

78





19







134

118

118

82

70

19/2.24

20







153

138

135

94

95

19/2.50

21

0.1

19/083



160

140

140

98





22

0.12

37/064



177

158

158

109





23







184

170

162

114

120

37/2.24

24

0.15

37/083



205

185

180

126





25







210

185

181

157

150

37/2.24

26







246

216

209

146

185

37/2.4

27

0.2

37.083



250

220

218

153





28







290

248

240

169

225

377/2.80

29

25

37/093



293

260

252

178





30

0.3

37/093



335

295

284

199





31







354

302

389

202

300

61/2.50

32







425

360

342

240





33







453

372





400

31/3.00

34

5

61/0.93



480

410









35







480

411





500

91/2.65

36







565

484





625

91/2.65

37

75

91/103



610

520









38

1.0

127/103



740

630









** Rating
Ambient Temperature 30^{o}C
For Ambient Temperature other than 30^{o}C
Rating should be multiplied by the following Rating Factors 25^{o}C
35^{o}C 40^{o}C 45^{o}C
Rating
Factor
1.13 96
69 47
In the above table current ratings (subject to voltage drop) have been
given for Copper conductor cables (in the new metric sizes as per I.S.
17531961) from this chart, the requires size of Aluminium conductor
can be established if either the Current Rating or the size of the
Copper Conductor is known.




ELECTRICAL
SYMBOLS
ELECTRICAL
STANDARDS
This is a list of a few standards in the
trade.
PANELBOARDS

Single Phase  3 Wire Systems

40A  100A  150A  225A 
400A
70A  125A  200A  300A  600 A

Three Phase  4 Wire Systems

60A  150A  225A  400A
125A  200A  300A  600A

SWITCHBOARDS
OR SWITCHGEARS

Single Phase

Three Phase

200 A
400 A
600 A
800 A
1200 A
1600 A
2000 A
2500 A
3000 A
4000 A

400 A
600 A
800 A
1200 A
1600 A
2000 A
2500 A
3000 A
4000 A

CIRCUIT BREAKERS AND FUSES

15 A
20 A
25 A
30 A
35 A
40 A
45 A
50 A
60 A

70 A
80 A
90 A
100 A
110 A
125 A
150 A
175 A
200 A

225 A
250 A
300 A
350 A
400 A
450 A
500 A
600 A
700 A

800 A
1000 A
1200 A
1600 A
2000 A
2500 A
3000 A
4000 A
5000 A
6000 A

For fuses only, additional
standard
sizes are 1, 3, 6, and 10.

GUTTERS AND WIREWAYS

2½" x 2½"
4" x 4"

6" x 6"
8" x 8"

10" x 10"

These sizes are available in
12", 24",
36", 48", and 60" lengths.

Disconnects

30A
60A
100a

200A
400A
600A

800A
1200A
1400A

1600A
1800A

PULL BOXES AND JUNCTION BOXES

4" x 4" x 4"
6" x 4" x 4"
6" x 6" x 4"
6" x 6" x 6"
8" x 6" x 4"
8" x 6" x 6"
8" x 6" x 8"
8" x 8" x 4"
8" x 8" x 6"
8" x 8" x 8"

10" x 8" x 4"
10" x 8" x 6"
10" x 10" x 4"
10" x 10" x 6"
10" x 10" x 8"
12" x 8" x 4"
12" x 8" x 6"
12" x 10" x 4"
12" x 10" x 6"
12" x 12" x 4"

12" x 12" x 6"
12" x 12" x 8"
15" x 12" x 4"
15" x 12" x 6"
18" x 12" x 4"
18" x 12" x 6"
18" x 18" x 4"
18" x 18" x 6"
24" x 18" x 6"
24" x 24" x 6"
24" x 24" x 8"

BUSWAY OR BUSDUCT

Single Phase

Three Phase

225 A
400 A
600 A
800 A
1000 A
1200 A
1350 A
1600 A
2000 A
2500 A
3000 A
4000 A
5000 A

225 A
400 A
600 A
800 A
1000 A
1200 A
1350 A
1600 A
2000 A
2500 A
3000 A
4000 A
5000 A

RUNNING
OVERLOAD UNITS
Kind
of Motor

Supply
System

Number
& Location of
Overload Units, such as
trip coils or relay

1
 Phase AC or DC

2wire,
1phase ac or dc,
ungrounded

1
in either conductor

1
 Phase AC or DC

2wire,
1phase ac or dc,
grounded neutral

1
in ungrounded conductor

1
 Phase AC or DC

3wire,
1phase ac or dc,
grounded neutral

1
in either ungrounded conductor

1
 Phase AC

any
3phase

1
in ungrounded conductor

2
 Phase AC

3wire,
2phase ac,
ungrounded

2,
one in each phase

2
 Phase AC

3wire,
2phase ac,
one conductor grounded

2
ungrounded conductors

2
 Phase AC

4wire,2phase
ac,
grounded or ungrounded

2,
one per phase in
ungrounded conductors

2
 Phase AC

5wire,
2 phase ac, grounded
neutral or ungrounded

2,
one per phase in any
ungrounded phase wire

3
 Phase AC

any
3phase

3,
one each phase *

* Exception: Where protected by other
approved means.
USEFUL FORMULAE
E
= Voltage / I = Amps /W = Watts / PF = Power
Factor / Eff = Efficiency / HP = Horsepower
AC/DC Formulas

To
Find

Direct Current

AC / 1phase
115v or 120v

AC / 1phase
208,230, or 240v

AC 3 phase
All Voltages

Amps
when
Horsepower is Known

HP x 746
E x Eff

HP x 746
E x Eff X PF

HP x 746
E x Eff x PF

HP x 746
1.73 x E x Eff x PF

Amps
when
Kilowatts is known

kW x 1000
E

kW x 1000
E x PF

kW x 1000
E x PF

kW x 1000
1.73 x E x PF

Amps
when
kVA is known


kVA x 1000
E

kVA x 1000
E

kVA x 1000
1.73 x E

Kilowatts

I x E
1000

I x E x PF
1000

I x E x PF
1000

I x E x 1.73 PF
1000

KilovoltAmps


I x E
1000

I x E
1000

I x E x 1.73
1000

Horsepower
(output)

I x E x Eff
746

I x E x Eff x PF
746

I x E x Eff x PF
746

I x E x Eff x 1.73 x PF
746


Three Phase Values

For 208 volts x 1.732, use 360
For 230 volts x 1.732, use 398
For 240 volts x 1.732, use 416
For 440 volts x 1.732, use 762
For 460 volts x 1.732, use 797
For 480 Volts x 1.732, use 831

E = Voltage / I = Amps /W
= Watts / PF = Power Factor / Eff = Efficiency / HP
= Horsepower
AC Efficiency and Power Factor
Formulas

To
Find

Single Phase

Three Phase

Efficiency

746 x HP
E x I x PF

746 x HP
E x I x PF x
1.732

Power
Factor

Input Watts
V x A

Input Watts
E x I x 1.732


Power  DC Circuits

Watts
= E xI

Amps
= W / E


Ohm's Law / Power Formulas


P = watts
I = amps
R = ohms
E = Volts


Voltage Drop Formulas

Single Phase
(2 or 3 wire)

VD =

2 x K x I x L
CM

K = ohms per mil foot
(Copper = 12.9 at 75°)
(Alum = 21.2 at 75°)
Note:

K value changes
with temperature. See Code chapter 9, Table 8

L = Length of conductor in feet
I = Current in conductor (amperes)
CM = Circular mil area of conductor

CM=

2K x L x I
VD

Three Phase

VD=

1.73 x K x I x L
CM

CM=

1.73 x K x L x I
VD

MOTOR FORMULAE
Calculating Motor Speed:
A squirrel cage induction motor is a
constant speed device. It cannot operate for any length of time at speeds below
those shown on the nameplate without danger of burning out.
To Calculate the speed of a
induction motor, apply this formula:
Srpm = 120
x F
P
Srpm = synchronous
revolutions per minute.
120 = constant
F = supply frequency (in cycles/sec)
P = number of motor winding poles
Example: What is the synchronous of a motor
having 4 poles connected to a 60 hz power supply?
Srpm = 120
x F
P
Srpm = 120 x 60
4
Srpm = 7200
4
Srpm = 1800 rpm
Calculating Braking Torque:
Fullload motor torque is calculated
to determine the required braking torque of a motor.
To Determine braking torque of a motor, apply this formula:
T = 5252
x HP
rpm
T =
fullload motor torque (in lbft)
5252 = constant (33,000 divided by 3.14 x 2 = 5252)
HP = motor horsepower
rpm = speed of motor shaft
Example: What is the braking torque of a
60 HP, 240V motor rotating at 1725 rpm?
T = 5252
x HP
rpm
T = 5252 x 60
1725
T = 315,120
1725
T = 182.7 lbft
Calculating Work:
Work is applying a force over a
distance. Force is any cause that changes the position, motion, direction, or
shape of an object. Work is done when a force overcomes a resistance.
Resistance is any force that tends to hinder the movement of an object.If an
applied force does not cause motion the no work is produced.
To calculate the amount of work
produced, apply this formula:
W =
F x D
W = work (in lbft)
F = force (in lb)
D = distance (in ft)
Example: How much work is required to
carry a 25 lb bag of groceries vertically from street level to the 4th floor of
a building 30' above street level?
W =
F x D
W = 25 x 30
W = 750 lb
Calculating Torque:
Torque is the force that produces
rotation. It causes an object to rotate. Torque consist of a force acting on
distance. Torque, like work, is measured is poundfeet (lbft). However,
torque, unlike work, may exist even though no movement occurs.
To calculate torque, apply this
formula:
T = F
x D
T = torque (in lbft)
F = force (in lb)
D = distance (in ft)
Example: What is the torque produced by a 60 lb
force pushing on a 3' lever arm?
T = F
x D
T = 60 x 3
T = 180 lb ft
Calculating Fullload Torque:
Fullload torque is the torque to
produce the rated power at full speed of the motor. The amount of torque a
motor produces at rated power and full speed can be found by using a
horsepowertotorque conversion chart. When using the conversion chart, place a straight edge
along the two known quantities and read the unknown quantity on the third line.
To calculate motor fullload torque,
apply this formula:
T = HP
x 5252
rpm
T = torque (in lbft)
HP = horsepower
5252 = constant
rpm = revolutions per minute
Example: What is the FLT (Fullload torque) of
a 30HP motor operating at 1725 rpm?
T = HP
x 5252
rpm
T = 30 x 5252
1725
T = 157,560
1725
T = 91.34 lbft
Calculating Horsepower:
Electrical power is rated in
horsepower or watts. A horsepower is a unit of power equal to 746 watts or
33,0000 lbft per minute (550 lbft per second). A watt is a unit of measure
equal to the power produced by a current of 1 amp across the potential
difference of 1 volt. It is 1/746 of 1 horsepower. The watt is the base unit of
electrical power. Motor power is rated in horsepower and watts.
Horsepower is used to measure the energy produced by an electric motor while
doing work.
To calculate the horsepower of a motor
when current and efficiency, and voltage are known, apply this formula:
HP = V
x I x Eff
746
HP = horsepower
V = voltage
I = curent (amps)
Eff. = efficiency
Example: What is the horsepower
of a 230v motor pulling 4 amps and having 82% efficiency?
HP = V
x I x Eff
746
HP = 230 x 4 x .82
746
HP = 754.4
746
HP = 1 Hp
Eff = efficiency
/ HP = horsepower / V = volts / A = amps / PF = power factor
Horsepower Formulas

To Find

Use Formula

Example

Given

Find

Solution

HP

HP = I X E X Eff.
746

240V, 20A, 85% Eff.

HP

HP = 240V x 20A x 85%
746
HP=5.5

I

I = HP x 746
E X Eff x PF

10HP, 240V,
90% Eff., 88% PF

I

I = 10HP x 746
240V x 90% x 88%
I = 39 A

To calculate the horsepower of a motor
when the speed and torque are known, apply this formula:
HP = rpm
x T(torque)
5252(constant)
Example: What is the horsepower of a
1725 rpm motor with a FLT 3.1 lbft?
HP = rpm
x T
5252
HP = 1725 x 3.1
5252
HP = 5347.5
5252
HP = 1 hp
Calculating Synchronous Speed:
AC motors are considered constant
speed motors. This is because the synchronous speed of an induction motor is
based on the supply frequency and the number of poles in the motor winding.
Motor are designed for 60 hz use have synchronous speeds of 3600, 1800, 1200,
900, 720, 600, 514, and 450 rpm.
To calculate synchronous speed of an
induction motor, apply this formula:
rpmsyn = 120
x f
Np
rpmsyn = synchronous speed (in
rpm)
f = supply
frequency in (cycles/sec)
Np = number of motor poles
Example: What is the synchronous speed of a
four pole motor operating at 50 hz.?
rpmsyn = 120
x f
Np
rpmsyn = 120 x 50
4
rpmsyn = 6000
4
rpmsyn = 1500 rpm
TRANSFORMER FORMULAE
To better understand the following
formulas review the rule of transposition in equations.
A multiplier may be removed from one side of an equation by making it a
division on the other side, or a division may be removed from one side of an
equation by making it a multiplier on the other side.
1. Voltage
and Current: Primary (p) secondary (s)
Power(p) = power (s) or Ep x Ip = Es x Is
A.

Ep =

Es x Is
Ip


B.

Ip =

Es x Is
Ep








C.

Is =

Ep x Ip
Es


D.

Es =

Ep x Ip
Is

2. Voltage
and Turns in Coil:
Voltage (p) x Turns (s) = Voltage (s) x Turns (p)
or Ep x Ts = Es x Ip
A.

Ep =

Es x Ip
Ts


B.

Ts =

Es x Tp
Ep








C.

Tp =

Ep x Ts
Es


D.

Es =

Ep x Ts
Tp

3. Amperes and Turns in Coil:
Amperes (p) x Turns (p) = Amperes (s) x Turns (s)
or Ip x Tp = Is x Ts
A.

Ip =

Is x Ts
Tp


B.

Tp =

Is x Ts
Ip








C.

Ts =

Ip x Tp
Is


D.

Is =

Ip x Tp
Ts
